1. Technical Field
The present invention relates to a method of forming a through hole in a layered structure that includes a layer having a photoimageable dielectric material.
2. Related Art
An electrical structure, such as a printed circuit board, typically includes a stack of cores. A core is a dielectric layer with metalization on either side. Such an electrical structure may include cores, such as 2 to 15 cores, laminated together with a layer of dielectric material between each pair of cores. Following lamination, a though hole may be formed through the thickness of the overall structure, such as by mechanical drilling or laser ablation, and then plated with metal to facilitate electrical coupling between various layers of the structure. Alternatively, the through hole may be formed incrementally by forming a via in a layer after the layer has been laminated onto the stack, such that the via thus formed is properly registered over the corresponding via in the preceding layer of the stack. Thus, the through hole may formed in either in one step or in a sequence of steps.
Drilling a through hole through a layered structure, such as by mechanical or laser drilling, is a very expensive step of the overall process and is often the most costly step. Moreover, it is not unusual for some of such drilled holes to generate a defect in the structure that necessitates discarding the structure, resulting in a yield loss coupled with loss of processing time. For example, the drilling may cause an unwanted pinhole or crack to form such that subsequent metallic plating of the structure results in plating of the pinhole which becomes a source of unwanted electrical shorting between conductive portions of the structure. Even greater costs may result from using the sequential method because a yield loss will occur at each step in which a via is formed with the cumulative cost growing nonlinearly as more layers are added.
A less costly method is needed to form a through hole in a layered dielectric structure.
The present invention provides a method for forming an electronic structure, comprising the steps of:
providing a layer that includes: a cylindrical volume of a photoimageable dielectric (PID) material, an annular volume of the PID material circumscribing the cylindrical volume, and a remaining volume of the PID material circumscribing the annular volume;
photolithograhically exposing the layer to radiation;
fully curing the annular volume by said radiation;
partially curing the remaining volume by said radiation; and
preventing curing of the cylindrical volume, wherein the PID material in the cylindrical volume remains uncured.
The present invention provides a method for forming an electronic structure having a through hole, comprising the steps of:
forming a layer that includes a via and an internal power plane having a hole therethrough, wherein a fully cured volume of a photoimageable dielectric (PID) material circumscribes the via, wherein a partially cured remaining volume of the PID material circumscribes the fully cured volume, and wherein a perimeter of the hole in the power plane surrounds the fully cured volume and circumscribes a portion of the remaining volume;
forming a first dielectric layer having a first via, wherein a cross-sectional area and shape of the first via is about the same as a cross-sectional area and shape of the via;
forming a second dielectric layer having a second via, wherein a cross-sectional area and shape of the second via is about the same as the cross-sectional area and shape of the via;
forming a layered stack, wherein the layer is nonadhesively sandwiched between the first dielectric layer and the second dielectric layer, and wherein the via is registered between the first via and the second via; and
fully curing the remaining volume, wherein the PID material of the partially cured volume is prevented by the fully cured volume from entering the via, wherein the layer becomes adhesively sandwiched between the first dielectric layer and the second dielectric layer, and wherein the electronic structure is formed such that the through hole comprises the first via, the via, and the second via.
The present invention provides a layer, comprising:
a cylindrical volume;
a fully cured annular volume of a photoimageable dielectric (PID) material circumscribing the cylindrical volume; and
a partially cured remaining volume of the PID material circumscribing the annular volume.
The present invention provides an electronic structure, comprising:
a layer that includes: a via, a fully cured volume of a photoimageable dielectric (PID) material circumscribing the via, and a partially cured remaining volume of the PID material circumscribing the fully cured volume; and
a power plane between a first surface of the layer and a second surface of the layer, wherein the power plane includes a hole therethrough, wherein a perimeter of the hole in the power plane surrounds the fully cured volume and circumscribes a portion of the remaining volume.
The present invention provides a method forming an electronic structure, comprising the steps of:
providing a layer that includes:
a cylindrical volume of a photoimageable dielectric (PID) material,
a first annular volume of the PID material circumscribing the cylindrical volume,
a second annular volume of the PID material circumscribing the first annular volume,
a remaining volume of the PID material circumscribing the second annular volume, and
a power plane between a first surface of the layer and a second surface of the layer, wherein the power plane includes a hole therethrough, and wherein a perimeter of the hole in the power plane circumscribes the second annular volume;
photolithograhically exposing the layer to radiation;
partially curing the first annular volume by said radiation;
fully curing the second annular volume by said radiation;
partially curing the remaining volume by said radiation; and
preventing curing of the cylindrical volume.
The present invention provides an electronic structure, comprising:
a layer that includes: a via, a first partially cured volume of a photoimageable dielectric (PID) material circumscribing the via, a fully cured volume of the PID material circumscribing the first partially cured volume, and a second partially cured remaining volume of the PID material circumscribing the fully cured volume; and
a power plane between a first surface of the layer and a second surface of the layer, wherein the power plane includes a hole therethrough, wherein a perimeter of the hole in the power plane circumscribes the fully cured volume.
The present invention advantageously forms a through hole in a layered structure having a layer that includes PID material, by a method which forms each layer and its via in isolation from the other layers, wherein a defect generated by formation of the via may result in discarding the layer without discarding the layered structure.
The present invention has the advantage of providing a fully cured annulus around a via within a layer of PID material, so that partially cured PID material cannot move into the via when the layered structure that includes the layer is subject to pressurization and/or elevated temperature.
The present invention has the advantage of forming photovias, which is a less expensive process than that of forming laser-drilled vias.
The preceding advantages facilitate lower fabrication costs, reduced cycle time, and improved quality assurance. Thus, the present invention has the overall advantage of providing an inexpensive method of forming a through hole in a layered dielectric structure having PID material in at least one layer.